Our eyes are never at rest. We are normally not aware that microscopic eye movements continually jitter the location of gaze, even when attending to a single point in the scene. It is known that visual percepts tend to fade when retina image motion is eliminated in the laboratory. However, it has also been hypothesized that, during natural viewing, fixational eye movements do more than prevent the visual scene from fading. Several findings from our recent NIH-funded research, including a spatial equalization of the temporal energy impinging on the retina during viewing of natural scenes, suggest that the fixational motion of the eye plays an important role in the processing of visual information. Building upon our recent results, this project addresses three fundamental questions: (Aim 1) How is spatial information encoded in the modulations of luminance resulting from fixational eye movements? (Aim 2) How is this information extracted and interpreted by the visual system? (Aim 3) Is the spatiotemporal redistribution of input energy flexible, so that it can be adjusted according to the task? To link the perceptual influences of fixational eye movements to their effect on the neural coding of visual information, this project integrates visual psychophysics in humans, analysis of retinal input, and neural modeling. Psychophysical experiments will rely on a flexible, sophisticated system for gaze-contingent display, which we have developed and extensively tested, to examine detection and discrimination performance under controlled retinal image motion. Statistical, computational, and modeling studies will examine the visual input signals experienced by subjects during high- acuity visual tasks and simulate the responses of neurons in the retina and lateral geniculate nucleus. These studies have the potential to force a radical shift in our understanding of retinal coding, replacing the traditional view of a purely sensory processing stage with a new view, in which perception and behavior are much more intimately tied than previously thought. Furthermore, a number of visual disorders manifest abnormal fixational eye movements. In addition to advancing our basic understanding of visual perception, a comprehension of the functional implications of fixational instability may lead to new treatment approaches for the visual impairments commonly associated with such conditions. PUBLIC HEALTH RELEVANCE: During natural viewing, humans continually perform microscopic eye movements. These movements are abnormal in various pathological conditions with reduced visual capabilities. By investigating the visual functions of microscopic eye movements, this project will advance the understanding of normal human vision as an integrated sensorimotor process and may open the way to new treatment approaches for the visual impairments commonly associated with such conditions.